Amiodarone is a new and valuable antiarrhythmic agent; however, its clinical efficacy is limited by significant and sometimes fatal pulmonary toxicity. Amiodarone pulmonary toxicity is associated with characteristic morphologic changes in the lung ("foamy" cytoplasmic inclusions/lamellar structures within the lung cells) which suggest the abnormal accumulation of phospholipids within the cytoplasm. Despite the life-threatening nature of this toxicity, the mechanism(s) underlying the development of these abnormal cytoplasmic inclusions by amiodarone is unknown. Our laboratory has developed a clinically relevant in vitro model of amiodarone pulmonary toxicity using cultured pulmonary edothelial cells (both bovine and human sources), and have successfully duplicated in vitro the characteristic morphologic changes described with the drug toxicity in human subjects. This model provides a unique opportunity to assess various hypotheses regarding the mechanism of amiodarone-induced lamellar inclusion formation and amiodarone-induced lung cell injury. Specific Aims of this proposal will 1) document the presence of these inclusions in cultured human pulmonary endothelial cells, 2) determine if the inclusions are reversible, 3) characterize the morphologic basis for the inclusions, 4) assess the hypothesis that inclusion formation is secondary to abnormal phospholipid metabolism, 5) assess if amiodarone toxicity is associated with significant (perhaps lethal) alterations in intracellular calcium, 6) quantify amiodarone-induced cell injury, and 7) assess factors or agents which may reduce amiodarone toxicity to cultured cells. Preliminary studies indicate that amiodarone alters phospholipid composition and turnover in the pulmonary endothelial cells, and in addition is a potent inhibitor of the endothelial cell phospholipase-A. It is highly likely these studies will improve our understanding of the mechanism(s) of amiodarone-induced morphologic changes and cell injury to cultured human pulmonary endothelial cells in vitro, and may well provide significant insight into the development of amiodarone pulmonary toxicity in vivo, and perhaps suggest new therapeutic strategies for this iatrogenic lung disorder.